Vision Glossary
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Vision Glossary
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TERMS AND DEFINITIONS AGC - Automatic Gain Control. A circuit for automatically controlling amplifier gain in order to maintain a constant output voltage with a varying input voltage within a predetermined range of input-to-output variation. Algorithm - A set of well-defined rules or procedures for solving a problem or providing an output from a specific set of inputs. Alpha Risk (ύ-risk) - The risk of rejecting good product. Ambient light - Light that is present in the environment of the imaging front end of a vision system and generated from outside sources. This light is usually treated as background noise by the vision system. Vision cameras should be shielded from ambient light. Analog-to-Digital Converter (A/D) - A device that converts an analog signal to a discrete series of digitally encoded numbers (signal) for computer processing. Angle of View - The angular range that can be focused within the image size. Small focal lengths give a wide angle of view, and large focal lengths give a narrow field of view. Aperture - The opening of a lens which controls the amount of light reaching the surface of the pickup device. The size of the aperture is controlled by the iris adjustment. By increasing the f stop number (f1.4, f1.8, f2.8, etc.) less light is permitted to pass to the pickup device. Artifact - An artificially created structure (by accident or on purpose), form or shape, usually part of the background, used to assist in measurement or object location. Area Array Camera - A solid state imaging device with both rows and columns of pixels, forming an array which produces a 2D image. Aspect Ratio - The ratio of width to height for the frame of the televised picture. 4:3 (or 1.333) for standard systems, 5:4 for 1K x 1K. Asynchronous (frame reset) - A camera characteristic which allows the return to top-of-frame to occur on demand, rather than synchronously following the 60 Hz power line scanning frequency. Attenuation A reduction in signal strength. Autofocus - The ability of an imaging system to control the focus of the lens to obtain the sharpest image on the detector. Edge crispness is a typical control variable. Auto Balance - A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction. Automatic Gain Control (AGC) - A process by which gain is automatically adjusted as a function of input or other specified parameter. Automatic Iris Lens - A lens in which the aperture automatically opens or closes to maintain proper light levels on the faceplate of the camera pickup device. Back Focal Distance - The distance from the rear most portion of the lens to the image plane. Backlighting - Placement of a light source behind an object so that a silhouette of that object is formed. It is used where outline information of the object and its features is important rather than surface features. Back Porch - That portion of the composite picture signal which lies between the trailing edge of the horizontal sync pulse and the trailing edge of the corresponding blanking pulse. Bandwidth - The number of cycles per second (Hertz) expressing the difference between the lower and upper limiting frequencies of a frequency band; also, the width of a band of frequencies. Bar Code - An identification system that employs a series of machine-readable lines of varying widths of black and white. Bar Code (2D) - An arrangement of rectangles and spaces that contains far more information than a traditional bar code. Barrel Distortion - An optical imperfection that causes an image to bulge convexly on all sides similar to a barrel. Beamsplitter - An optical device which divides one beam into two or more separate beams. A simple coated piece of glass in the optical path might reflect 60% of the light down onto the object, while allowing the other 40% to pass. Beta Risk (-risk) - The risk of accepting bad or defective product. Binary image - A black and white image represented as a single bit containing either zeros or ones, in which objects appear as silhouettes. The result of backlighting or thresholding. Blob - A single, connected region in a binary or grayscale image. Blob Analysis - Identification of segmented objects in an image based on their geometric features. Borescope - A device for internal inspection of difficult access locations such as pipes, engines, rifle barrels and pipes. Its long narrow tube contains a telescope system with a number of relay lenses. Light is provided via the optical path or fiber bundles. A 45-degree mirror at the end allows inspection of tube walls Blooming - The defocusing of regions of the picture where the brightness is at an excessive level. Calibration - The act of relating X and Y pixel spacing to a known or predetermined pixels per unit length (i.e. inch, mm) factor. Coatings - Light is lost by reflection from optical surfaces that are intended to be refractors only. Very thin coatings on the lens surfaces effectively reduce this loss. This can be seen as a blue or violet hue on the lens surface. C Mount - A television camera lens mount of the 16-mm format, 1 inch in diameter with 32 threads per inch. CCTV lenses are available in two different lens mounts. "C-mount" lenses have a flange back distance of 17.5mm Vs 12.5mm for "CS-mount" lenses. Many of today's cameras can accept either type of lens, but it is important to make sure that camera and lens are compatible and set up properly. C-mount lenses can be used on CS-mount cameras by utilizing a 5mm adapter or adjusting the camera for C-mount lenses. Because of the shorter back focal distance, CS-mount lenses can only be used on CS-mount cameras. Your picture will be out of focus if you use a CS-mount lens on a C-mount camera. CCTV - The abbreviation for Closed-Circuit Television. Centroid In machine vision, this is the center of mass ( usually of the white pixel count ) or the center of location mark or fiducial. Character Recognition (OCR) - Imaging and recognizing individual characters in a scene. Also called Optical Character Recognition. Character Verification (OCV) - Imaging and verifying the correctness, quality and legibility of known characters in an image. Also Optical Character Verification. Charge-Coupled Device (CCD) - For imaging devices, a self-scanning semiconductor array that utilizes MOS technology, surface storage, and information transfer by shift register techniques. Chroma - That qualities of color which embraces both hue and saturation. White, black, and grays have no chroma. Chroma Control - A control of color television receiver that regulates the saturation (vividness) of colors in a color picture. Chroma Detector - Detects the absence of chrominance information in a color encoder input. The chroma detector automatically deletes the color burst from the color encoder output when the absence of chrominance is detected. Chromatic Aberration - An optical defect of a lens which causes different colors or wave lengths of light to be focused at different distances from the lens. It is seen as color fringes or halos along edges and around every point in the image. Chromaticity - The color quality of light which is defined by the wavelength (hue) and saturation. Chromaticity defines all the qualities of color except its brightness. Chrominance - A color term defining the hue and saturation of a color. Does not refer to brightness. Chrominance Signal - The portion of the NTSC color television signal that contains the color information. Clamp - A device that functions during the horizontal blanking or synchronizing interval to fix the level of the picture signal at some predetermined reference level at the beginning of each scanning line. Clamping - The process that establishes a fixed level for the picture level at the beginning of each scanning line. Clipping - The shearing off of the peaks of a signal. For a picture signal, this effects the positive (white). Coaxial Cable - A particular type of cable capable of passing a wide range of frequencies with very low signal loss. Color Burst - That portion of the composite color signal, comprising a few cycles of a sine wave of chrominance subcarrier frequency, which is used to establish a reference for demodulating the chrominance signal. Color Camera Color cameras use either a single chip sensor or a three-chip sensor to sense red, blue, and green. Color Edging - Extraneous colors appearing at the edges of colored objects, and differing from the true colors in the object. Color Encoder - A device which produces an NTSC color signal from separate R, G, and B video inputs. Color Fringing - Spurious colors introduced into the picture by the change in position of the televised object from field to field. Color Purity - The degree to which a color is free of white or any other color. Color Saturation - The degree to which a color is free of white light. Color Sync Signal - A signal used to establish and to maintain the same color relationships that are transmitted. Color Transmission - The transmission of a signal that represents both the brightness values and the color values in a picture. Composite Video Signal - A camera signal that is produced by combining both a video or picture signal with horizontal and vertical synch and blanking, signals. Condenser Lens - Used to collect and redirect light for the purpose of illumination. Often used to collect light from a small source and project it evenly onto an object. Connectivity Analysis - A routine used to determine which pixels are interconnected and part of the same object or region. The results are used for blob analysis. Contrast - The difference of light intensity between two adjacent regions in the image of an object. Often expressed as the difference between the lightest and darkest portion of an image. Contrast between a flaw (or a feature) and its background is the goal of illumination. Contrast Enhancement - Stretching of the gray level values between dark and light portions of an image to improve both visibility and feature detection. Convergence - The crossover of the three electron beams of a three-gun tri-color picture tube. Convolution - Superimposing an m x n operator (usually a 3x3 or 5x5 mask) over an area of the image, multiplying the points together, summing the results to replace the original pixel with the new value. This operation can be performed on the entire image or regions of interests to enhance edges, features, remove noise and other filtering operations. Correlation - A mathematical measure of the similarity between images or areas within an image. Pattern matching, or correlation of an X by Y array size template to the same size image, produces a scalar number, the percentage of match. The template is usualy walked through a larger array to find the highest match. Crosstalk - An undesired signal from a different channel interfering with the desired signal. Darkfield Illumination - Lighting of objects, surfaces or particles at very shallow or low angles, so that light does not directly enter the optics. Objects are bright with a dark background. This grazing illumination causes specular reflections from abrupt surface irregularities. DC Type Lens - An auto-iris lens with an internal circuit which receives voltage and a video signal from the camera to adjust the iris. Depth of Field - The front to back zone in a field of view that is in focus in the televised scene. With a greater depth of field, more of the scene, near to far, is in focus. Increasing the f-stop number increases the depth of field of the lens. Therefore, the lens aperture should be set at the highest f-stop number usable with the available lighting. The better the lighting, the greater the depth of field possible. In other words, the depth of field is the area in front of the camera that remains in focus. The larger the f-number the greater is the depth of field. Depth of Focus - The range of sensor-to-lens distance for which the image formed by the lens is clearly focused. Diffused lighting - Scattered soft lighting from a wide variety of angles used to eliminate shadows and specular glints from profiled, highly reflective surfaces. Diffused lighting minimizes surface texture. Digital Area Scan Cameras - These cameras have an on board analog to digital converter that converts the light level of each pixel on the CCD array into a digital word. The advantages to digital cameras are that the image data can be transmitted quicker, without degradation, and are less susceptible to noise. Digital Line Scan Cameras - These cameras have an on board analog to digital converter that converts the light level of a single line (row) of pixels into a digital word. They send the data out one line at a time. These cameras are high-resolution cameras capable of very high data rates. Linescan cameras require a very intense light and an encoder to track the part while it is moving under the camera. Distortion - The deviation of the received signal waveform from that of the original transmitted waveform. Dynamic Range - The difference between the maximum acceptable signal level and the minimum acceptable signal level. Edge - A change in pixel values exceeding some threshold amount. Edges represent borders between regions on an object or in a scene. Edge Detection - The ability to determine the true edge of an object. EIA Sync - The signal used for the synchronizing of scanning specified in EIA Standards RS-170, RS-330, RS-343, or subsequent issues. Extension Tube - A kit consisting of various size spacers that are used between the lens and the camera to reduce the lens minimum object distance. Extension tubes are not recommended for zoom lenses due to loss of tracking. Feature Extraction - Determining image features by applying feature detectors to distinguish or segment them from the background. Fiber Optics - Transparent fibers all bundled together parallel to one another. This bundle of fibers has the ability to transmit a light from one of its surfaces to the other around curves and into otherwise inaccessible places with an extremely low loss of definition and light. Fiberscope - An optical instrument similar to a borescope, but uses a flexible, coherent fiber or bundle (usually silicon), an objective lens and an eyepiece or camera. Fiducial - A line, mark or shape used as a standard of reference for measurement or location. Field - One of two parts of a video frame in an interlaced scanning system. One even field and one odd field compromise one video frame. Field of View - The maximum angle of view that can be seen through a lens or optical instrument. F-Number - The f-number indicates the brightness of the image formed by lens, controlled by the iris. A smaller f-number means a brighter image. Focal Length - The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite distance from the camera is produced. The focal length determines the size of the image and the angle of the field of view seen by the camera through the lens. That is the distance from the center of the lens to the pickup device. Frame - The total area (2 fields on an RS-170 signal) that is scanned while the camera signal is not blanked. Frame Frequency - The number of times per second that the frame is scanned. The U.S. standard is 30 frames per second. Frame Buffer - Image memory in a frame grabber. Frame Grabber - A device that interfaces with a camera and, on command, samples the video, converts the sample to a digital value and stores that number in a computer's memory. Frame Transfer - A CCD imager where an entire matrix of pixels is read into storage before being output from the camera. Frequency Interlace - The method by which color and black and white sideband signals are interwoven within the same channel bandwidth. Front Lighting - The use of illumination on the camera side of an object so that the surface features can be observed. Front Porch - The portion of a composite picture signal that lies between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding sync pulse. F/Stop - A term used to indicate the speed of a lens. The smaller the f-number, the greater the amount of light passing through the lens. Gauging - In machine vision, non-contact dimensional examination of an object. Gain - An increase in voltage or power, usually expressed in dB. Gamma - A numerical value, or the degree of contrast in a television picture, which is the exponent of that power law which is used to approximate the curve of output magnitude versus input magnitude over the region of interest. Gamma Correction - To provide for a linear transfer characteristic from input to output device. Genlock - A device used to lock the frequency of an internal sync generator to an external source. Ghost - A spurious image resulting from an echo. Gray Scale - Variations in value from white, through shades of gray, to black (usually 256, 8 -bit image) on a television screen. The gradations approximate the tonal values of the original image picked up by the machine vision camera. Hue - Corresponds to colors such as red, blue, etceteras. Image Intensifier - A device coupled by fiber optics to a camera image pickup sensor to increase sensitivity. Impedance (input or output) - The input or output characteristic of a system component that determines the type of transmission cable to be used. The cable used must have the same characteristic impedance as the component. Expressed in ohms. Video distribution has standardized on 75-ohm coaxial and 124-ohm balanced cable. Incident Light - The light that falls directly on an object. Interline Transfer - A technology of CCD design, where rows of pixels are output from the camera. The sensor's active pixel area and storage register are both contained within the active image area. Interlaced Scanning - A scanning process in which all-odd lines then all even lines are alternately scanned. Adjacent lines belong to different fields and are collected at different times. So, a moving object may appear in a slightly different location on odd/even fields. Iris - An adjustable aperture built into a camera lens to permit control of the amount of light passing through the lens. Jitter - Small, rapid variations in a waveform due to mechanical disturbances or to changes in the characteristic of components. Supply voltages, imperfect synchronizing signals, circuits, etc. Lens Preset Positioning - Follower Pots are installed on lens that allows feedback to the controller information relevant to zoom and focus positioning allowing the controller to quickly adjust to a preselected scene and arrive in focus at the proper focal length automatically. Lens Speed - Refers to the ability of a lens to transmit light, represented as the ratio of the focal length to the diameter of the lens. A fast lens would be rated <f/1.4; a much slower lens might be designated as> f/8. The larger the f number, the slower the lens. Level Control - Main iris control. Used to set the auto-iris circuit to a video level desired by the user. After set-up, the circuit will adjust the iris to maintain this video level desired by the user. After set-up, the circuit will adjust the iris to maintain this video level in changing lighting conditions. Light - Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. Line Scan Camera - A solid state video camera consisting of a single row of pixels. The sensor captures a row of data, reads it out, then captures the next row of data. Loss - A reduction in signal level or strength, usually expressed in dB. Power dissipation serving no useful purpose. Low-Frequency Distortion - Distortion effects which occur at low frequencies. In television, generally considered as any frequency below the 15.75-kHz line frequency. Lumen (LM) - The unit of luminous flux. Lumen/FT2 - A unit of incident light. It is the illumination on a surface one square foot in area on which a flux of one lumen is uniformly distributed, or the illumination at a surface all points of which are at a distance of one foot from a uniform source of one candela. Luminance Signal - That portion of the NTSC color television signal which contains the luminance or brightness information. Lux - International System (Sl) unit of illumination in which the meter is the unit of length. One lux equals one lumen per square meter. Machine Vision - The use of devices for optical non-contact sensing to automatically receive and interpret an image of a real scene, in order to obtain information and/or control machines or processes Manual Iris Lens - A lens with a manual adjustment to set the iris opening (F-stop) in a fixed position. Minimum Object Distance (M.O.D.) - The closest distance a given lens will be able to focus upon an object. This is measured from the vertex (front) of the lens to the object. Wide-angle lenses generally have a smaller M.O.D. than large focal length lenses. Modulation - The process, or results of the process, whereby some characteristic of one signal is varied in accordance with another signal. The modulated signal is called the carrier. The carrier may be modulated in three fundamental ways: by varying the amplitude, called amplitude modulation; by varying the frequency, called frequency modulation; by varying the phase, called phase modulation. Monochrome - A gray scale image. Morphology - Image algebra group of mathematical operations based on manipulation and recognition of shapes. Also called mathematical morphology. Operations may be performed on either binary or gray scale images. Opaqueness - The degree to which an object does not transmit light. ND Filter - A filter that attenuates light evenly over the visible light spectrum. It reduces the light entering a lens, thus forcing the iris to open to its maximum. Noise - The word "noise" originated in audio practice and refers to random spurts of electrical energy or interference. In some cases, it will produce a "salt-and-pepper" pattern over the televised picture. Heavy noise is sometimes referred to as "snow". Non-Composite Video - A video signal containing all information except sync. Non-Interlaced Scan (sequential scan) - The camera begins at the start of the frame and lines are scanned in their natural order (1,2,3,4 . etc.). NTSC - Abbreviation for National Television Systems Committee. A committee that worked with the FCC in formulating standards for the present day United States color television system. Pan and Tilt - A device upon which a camera can be mounted that allows movement in both the azimuth (pan) and in the vertical plane (tilt). Pan/Tilt Preset Positioning - Follower pots are installed on pan/tilt unit to allow feedback to the controller and provides information relevant to horizontal and vertical positioning, allowing the controller to quickly adjust to a pre-selected scene automatically. Pattern Recognition - A process that identifies an object based on analysis of its features. Peak-to-Peak - The amplitude (voltage) difference between the most positive and the most negative excursions (peaks) of an electrical signal. A full video signal measures one-volt peak to peak. Pinhole Lens - Lens used for applications where the camera/lens must be hidden. Front of lens has a small opening to allow the lens to view an entire room through a small hole in the wall. Pixel - Short for Picture Element. A pixel is the smallest area of a television picture capable of being delineated by an electrical signal passed through the vision system. The number of picture elements (pixels) in a complete picture, and their geometric characteristics of vertical height and horizontal width, provides information on the total amount of detail that the can be displayed. Polarizer - An optical device that converts natural or unpolarized light into polarized light by selective absorption of rays in one direction, and passing of rays perpendicular to the polarizing medium. Pre-Position Lenses - Zoom lenses that utilize a variable-resistor (potentiometer) to indicate zoom/focus position to the lens controller. After initial set-up, this allows the operator to view different pre-set areas quickly without having to readjust the zoom and focus each time. Primary Colors - The colors wherein no mixture of any two can produce the third. In color television these are the additive primary colors red, blue and green. Progressive Scan - The progressive scan format outputs data from the camera (the signal) in sequential order as it is scanned. The scan format produces a full frame of video in a continuous stream, rather than half the image per output sequence(interlaced image) in traditional RS-170 CCD cameras. Standard RS-170 video is interlaced and output in two separate fields, generating essentially half the image at a time. Real Time Processing - In machine vision, the ability of a system to perform a complete analysis and take action on one part before the next one arrives for inspection. Resolution (horizontal) - The amount of resolvable detail (vertical rows of pixels) in the horizontal direction in an image. Resolution (vertical) - The amount of resolvable detail (horizontal lines of pixels) in the vertical direction in an image. Roll - A loss of vertical synchronization that causes the picture to move up or down on a receiver or monitor. RS-170 - The Electronic Industries Association (EIA) standard governing monochrome television studio electrical signals. The broadcast standard of 30 complete images per second. RS-232-C - The Electronic Industries Association (EIA) standard governing serial communications over a twisted pair. Good to about 150 feet. RS-330 - Standard governing color television studio electrical signals. RS-422; RS-423; RS-449 - The Electronic Industries Association (EIA) standards for serial communication protocols intended to gradually replace the widely used RS-232-C standard. Saturation - The degree to which a color is diluted with white light or is pure. The vividness of a color, described by such terms as bright, deep, pastel, pale, etc. Saturation is directly related to the amplitude of the chrominance signal. Sensitivity - In television, a factor expressing the incident illumination upon a specified scene required to produce a specified picture signal at the output terminals of a television camera. Shutter - Ability to control the integration time to the image sensor too less than 1/60 second; e.g.: stop motion of moving traffic. Signal-to-Noise Ratio - The ratio between useful television signal and disturbing noise or snow. Snow - Heavy random noise. Specular Reflections Light rays come from a single direction and are bright. They are unreliable because a small change in angle between the illuminator and the object may cause the specular reflection to disappear. Standard Minimum Signal - 1000 microvolts at 75 ohms (0dB mV) in RF systems; 0.7-VPP non-composite, 1-VPP composite in video systems. Strobe Duration - The amount of time, expressed in microseconds, during which the flash lamp (strobe) is at 90% intensity. Strobe Light - Brief flashes of light for observing an object during a short interval of time, typically used to "stop" movement and resulting image blur. Strobes may use xenon flash tubes, banks of LEDs or a laser to illuminate the scene Structured Light - Points, lines, circles, sheets and other projected configurations used to directly determine shape and/or range information by observing their deformation as it intersects the object in a known geometric configuration. Subpixel Resolution - Mathematical techniques used on gray scale images to resolve an edge location too less than one pixel. Sync Generator - A device for generating a synchronizing signal. Sync Signal - The signal employed for the synchronizing of scanning. Tearing - A term used to describe a picture condition in which groups of horizontal lines are displaced in an irregular manner. Telecentric Lens A lens that provides constant magnification at any object distance. They make accurate dimensional measurements over a larger range than conventional lens. Also, telecentric lenses view the whole field form the same perspective. Thus, a deep round hole looks round at the top and bottom of the hole. Template Matching - A form of correlation used to find out how well two images match. Thresholding - The process of converting gray scale image into a binary image. If the pixel's value is above the threshold, it is converted to white. If below the threshold, the pixel value is converted to black. Throughput Rate - The maximum parts per minute inspection rate of a system. Tracking - The ability of a zoom lens to remain in focus during the entire zoom range from wide angle to telephoto position. Variable Scan Camera - This is a non RS-170 camera that sends out sync and clock signals to the frame grabber that allows for the camera scan rate to vary. Video Band - The frequency band width utilized to transmit a composite video signal. Video Signal (Non-Composite) - The picture signal. A signal containing visual information and horizontal and vertical blanking (see also Composite Video Signal) but not sync. Xenon Strobe - A gas filled electronic discharge tube, useful for high speed, short duration illumination for inspection. Y Signal - A signal transmitted in color television containing brightness information. This signal produces a black and white picture on a standard monochrome receiver. In a color picture it supplies fine detail and brightness information. Zoom Lens - A lens system that may be effectively used as a wide angle, standard, or telephoto lens by varying the focal length of the lens. Zoom Ratio - The ratio of the starting focal length (wide position) to the ending focal length (telephoto position) of a zoom lens. A lens with a 10X-zoom ratio will magnify the image at the wide-angle end by 10 times. |
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